1. Field of the Invention
The invention relates to a communication terminal in a radio communication system such as a mobile communication system, and particularly to a communication terminal in a radio communication system, in which a base station assigns terminal identification information to individual communication terminals (for example, portable phones) in its area, which are to be distinguished from one another, to make connections of communication channels.
2. Description of Related Art
To distinguish communication terminals (called “terminals” hereunder) from one another, various kinds of systems have been proposed that dynamically allocate a terminal identifier which is effective for a limited period of time. There is a system in which as a terminal identifier such as a DHCP (Dynamic Host Configuration Protocol) protocol of RFC (Requests For Comments) 2131, an IP (Internet Protocol) address is given, or a system in which an UATI (Unicast Access Terminal Identifier) is used as a terminal identifier such as HRPD (High Rate Packet Data) that is standardized in 3GPP2 (3rd Generation Partnership Project 2) in a radio environment.
In a system in which a terminal identifier is utilized to identify these kinds of individual terminals, when a disagreement occurs in an identifier assigned to a terminal and a radio communication base station (called a “base station” hereunder), an interrupted condition for communication occurs because of failure to recognize the individual terminals. In order to overcome the interrupted condition for communication, a limitation on effective time for the identifier is set. To be specific, an effective time limit is provided for each process of communication protocols. When the process has not been completed within the time limit, the identifier is invalidated. Alternatively, when the identifier is confirmed on the side of the base station and is determined to be invalid, a process of re-assignment of an identifier is conducted.
The HRPD is disclosed, for example, in Japanese Patent Publication No. 2003-92782.
The method of improving the state by providing an effective time limit for the terminal identifier as shown above has the following problems. That is, with respect to a system using a radio environment such as the HRPD, base stations and terminals are required to reduce traffic from the point of view of efficient use of radio resources. For that reason, since a method of reducing a period of time for interrupted conditions by shortening an effective period of time for the terminal identifier brings about an increase in communication traffic, this is not desirable.
It is effective for a base station to detect an invalid identifier. However, since all the base stations with which a terminal communicates are required to implement this function, in the case in which a connection is established between a base station that does not respond to the function, proper recovery of communication conditions is not carried out, which is a problem.